The human dopamine transporter (hDAT) is the plasmalemmal membrane protein that mediates the inactivation of released dopamine (DA) through its reuptake. hDAT is the major molecular target responsible for the rewarding properties and abuse potential of amphetamine (AMPH) and related psychostimulants. AMPH, as a result of its ability to reverse the inward transport of DA, is believed to induce DA efflux and therefore increases extracellular DA levels. However, the underlying mechanism of this AMPH action is unclear: Hypothesis: Through its functional interaction with hDAT, AMPH uniquely stimulates both an increase in intracellular ion concentrations and the activity of calcium/calmodulin-dependent protein kinase II (CaMKII), leading to the direct or indirect phosphorylation of the hDAT N-terminus and subsequent DA efflux. Two specific aims address this hypothesis: 1) To identify differences between AMPH and other hDAT substrates in their ability to stimulate changes in intracellular ion concentrations (Na+, CI-, Ca2+) that promote DA efflux; and 2) to determine whether AMPH-induced activation of CaMKII regulates hDAT- mediated DA efflux via N-terminal phosphorylation of the transporter. [unreadable] [unreadable] [unreadable]